Causes and Risk Factors of Myasthenia Gravis

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Myasthenia gravis (MG) is a chronic neuromuscular autoimmune disease that causes skeletal muscles to weaken, particularly after strenuous activity. The muscles in the eyelids and those attached to the eyeball are commonly the first (and sometimes only) muscles affected in myasthenia gravis. Other muscles that may become weak include jaw, limb, and even breathing muscles.

There is no cure for MG, but some treatments are available that can help to alleviate its symptoms. Although myasthenia gravis can be diagnosed at any age—including during childhood—it is most often seen in women less than age 40 and in men more than age 60. 

woman at the doctor

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Common Causes

The cause of MG is an autoimmune reaction in which the body’s immune system mistakenly attacks specific proteins in the muscles.

When a person has MG, antibodies—called acetylcholine receptor (AChR) antibodies—misguidedly attack the receptors for acetylcholine, a chemical messenger released by nerve cells to stimulate muscle contractions. As a result of the interference with the transmission of nerve-to-muscle signaling, muscle weakness develops.

A person with MG can also have antibodies—called muscle-specific receptor tyrosine kinase (MuSK) antibodies—produced against proteins located on the surface of the muscle membrane.

Causes of Immunodeficiency

The specific underlying cause of the abnormal immune response, which occurs in people with MG, is not well known.

However, studies have discovered a link between people with MG and abnormalities in the form of enlargement of the thymus gland.

According to Harvard Health, nearly 80% of people with MG have distinct abnormalities of the thymus gland.

Causes of Ocular Myasthenia Gravis

Ocular MG is a type of MG that involves the muscles that move the eyes and eyelids. This causes:

  • Double vision
  • Difficulty focusing the eyes
  • Drooping eyelids
myasthenia gravis

Verywell / Alexandra Gordon

Nearly 15% of people with MG only have ocular MG gravis.

Over time, if weakness develops in other muscles in the body, the type of myasthenia gravis may change from ocular myasthenia gravis to generalized myasthenia gravis.

Causes of Transient Neonatal Myasthenia Gravis

Some newborns (with mothers who have MG) develop muscle weakness temporarily. This is a condition called transient neonatal MG.

The cause of transient neonatal myasthenia gravis is antiacetylcholine receptor antibodies that travel through the placenta to the unborn child during pregnancy.

It takes about two months for the mother’s antibodies to be cleared from the baby’s system, resulting in the subsiding of muscle weakness in the baby.

Genetics

Most cases of MG do not involve a family history of the disease; MG is thought to occur sporadically for unknown reasons. But that is not always the case. In 5% of those with myasthenia gravis, there is a family member with some type of autoimmune disorder.

Also, genetics are thought to possibly play a role in predisposing a person to MG. This is because specific antigens—called human leukocyte antigens—which are genetically determined, are thought to affect a person’s risk of getting certain types of diseases.

Commonly, people with MG develop other types of autoimmune disease, including thyroid disorders and systemic (involving the entire body) lupus erythematosus.

Individuals with MG also have an increased frequency of certain genetically determined human leukocyte antigens (HLAs), suggesting that genetic predisposition may play some role in the development of myasthenia gravis.

Genetic Predisposition for Autoimmune Diseases

Unlike many other types of disorders, MG is not considered a disease that is directly inherited, but rather, there may be a genetic predisposition for autoimmune diseases.



Cardiovascular Involvement

In addition to its impact on the neuromuscular system, MG impacts other organs and systems of the body, The disease is known to cause a high prevalence of heart problems in 10% to 15% of those with MG who also have thymoma.

Cardiovascular involvement may include:

According to a 2014 study, the heart muscle is a target for autoimmune inflammation in MG. In addition to thymoma posing a risk factor to heart muscle involvement in those with MG, other factors may influence this risk as well, including:

  • Advancing age
  • The presence of anti-Kv1 antibodies

Lifestyle Risk Factors

A 2018 Swedish study found that those with late-onset disease had a more disadvantageous pattern of lifestyle-related risk factors, and a higher rate of:

  • Smoking
  • Obesity
  • Physical activity
  • Insufficient diet (including a lower rate of fish consumption)

General Risk Factors

General risk factors found to increase the chance of a person getting MG include:

  • Being a woman between the ages of 20 to 30
  • Being a man between the ages of 60 to 70
  • Having specific genetic markers called HLA-B8 or DR3
  • Neonates (newborn infants) with mothers who have abnormal antibodies that have entered the baby’s body via the placenta during pregnancy

Prevention Measures

Although the causes of MG are unknown and cannot be changed, flare-ups may be controlled by implementing some lifestyle changes. 

If you have been diagnosed with MG, many lifestyle changes may help prevent flare-ups and lower the chances of worsening symptoms, these lifestyle changes include:

  • Getting plenty of sleep
  • Taking rest periods when needed
  • Avoiding strenuous or exhausting activities
  • Staying out of the extreme heat and cold
  • Coping with emotional stressors
  • Avoiding infections when possible
  • Working with your healthcare provider to avoid drugs that worsen MG

A Word From Verywell

At Verywell Health, we know that being diagnosed with a condition such as MG is no small undertaking. The condition is lifelong, but early diagnosis and intervention are the keys to effectively managing the disease on a long-term basis. 

If you suspect you may have myasthenia gravis, it’s important to call your healthcare provider right away.

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9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Harvard Health. Myasthenia gravis. Updated December 2018.

  3. Myasthenia Gravis Foundation of America. Learn more about MG.

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  5. National Organization for Rare Disorders. Myasthenia gravis.

  6. Genetic and Rare Diseases Information Center. Myasthenia gravis. Updated April 3, 2018.

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  8. Suzuki S, Utsugisawa K, Nagane Y, Suzuki N. Three types of striational antibodies in myasthenia gravis. Autoimmune Diseases. 2011;2011:1-7. doi:10.4061/2011/740583

  9. Westerberg, E. UPPSALA UNIERSITET. Environmental factors of importance in myasthenia gravis. Updated 2018.